It's simplistic, but for what it is, it's enjoyable. A couple of thoughts:

-In the first level, I couldn't figure out that the blue area was the goal. I thought I had died because the menu popped up asking me to restart. I'd say either put "Next Level" as the top choice or, even better, just start the next level automatically.

-The controls (at least on an iPad) are somewhat uncomfortable for me. I'd prefer it if the left/right buttons were closer together and/or closer to the left edge.

-While the starry background is cool and helps spice up the graphics, I think it becomes a detriment when you start facing enemies that shoot at you since it makes the bullets even harder to see.

Oh, yeah, sorry if I wasn't clear: I really do like the starry background in the initial stages. It just made it hard to see the enemy bullets in later stages. Thus, I think bigger or shinier bullets is a fine solution.